Some devices can't drive larger headphones. Some have crappy DACs. The Aqua Headphone Amplifier
is designed to solve both these problems. It connects via Lightning or
MicroUSB and uses a 24-bit/192kHz DAC from AKM to provide excellent
audio quality, as well as a 60mW amplifier to make sure your cans are
getting plenty of power. There's also an onboard USB audio controller, a
status LED, and a play & pause button, all housed in an angular
machined aluminum case weighing just 16 grams.